Conventional evaporators are typically formed from a plurality of tubes contained within a shell. Feed liquid is passed within the evaporator tubes, and hot gases or liquids are passed on the outside of the evaporator tubes to heat the tubes. Conventional evaporator tubes are configured such that a feed liquid to be heated forms a liquid film on inner surfaces of a conduit. The outer surfaces of the conduit is typically surrounded with steam.
There exist numerous types of evaporators. For example, there exist conventional falling film evaporators, shown by way of example and not limitation at http://www.gea.com/global/en/products/falling-film-evaporator.isp, rising film evaporators, shown by way of example and not limitation at https://en.wikipedia.org/wiki/Rising film evaporator, wiped film evaporators shown by way of example and not limitation at http://lcicorp.com/thin film evaporators thin film wiped film evaporator/, and other thin film heat and mass transfer devices. These devices use flow geometries that position process feed fluids within vertical tubes (or a cylinder) and include heating systems, which typically uses steam, positioned on the outside of the tubes and within an outer housing, which is referred to as a shell. In a falling film evaporator, a thin liquid film flows along the inside wall of the vertical tubes from top to bottom and in the case of a rising film evaporator, the liquid film is pushed upwards from the bottom to top.
These systems experience a number of limitations. In particular, vapor is formed on the inside of the tubes leaving concentrate at the outlet of the conduit. Formation of the vapor within the tube increases the pressure within the tube, which increases the boiling point. In addition, conventional systems experience scale formation and buildup on the interior surfaces of the tubes, which also negatively affects heat transfer efficiency. Thus, a need exists for a more efficient heat and mass transfer system.